In recent years, the rate of data transfer is made higher in disk drives for recording or reproducing data, such as CD-ROM drives, DVD-ROM drives and CD-R/RW drives. In accordance with this trend, it has become absolutely necessary to rotate disks at high speed.
Many disks on the market are unbalanced disks having an offset in mass balance owing to uneven thickness or the like (disks with offset centers of gravity). If such a disk is rotated at high speed, the imbalance force of the disk acts significantly and causes vibration. The vibration is transmitted to the entire disk drive, thereby making stable data recording and reproduction impossible and causing noise owing to the vibration. In addition, the vibration shortens the life of its motor. Furthermore, in the case when the disk drive is built in a computer, the vibration is transmitted to other peripheral devices and adversely affects them.
For this reason, in raising the rate of data transfer by rotating a disk at high speed, it is absolutely necessary to restrict vibration owing to the imbalance of the disk. Various measures have been taken to cancel the imbalance.
<Explanation of FIG. 29>
A conventional disk drive capable of canceling an imbalance and having already been applied by the applicant of the present invention will be described below.
FIG. 29 is a view showing a disk drive having a conventional balancer.
The balancer of the disk drive shown in FIG. 29 is provided with a ring-shaped hollow section 4 and can rotate integrally with a disk 5 loaded into the disk drive.
Inside the ring-shaped hollow section 4, plural magnetic balls 1 are movably accommodated, and the ring-shaped hollow section 4 is made coaxial with the rotation center shaft 3 of a spindle motor 2. The ring-shaped hollow section 4 is formed inside a damper 6, and the disk 5 is held between the clamper 6 and a turntable 7. The external peripheral face 9 of the magnet 8 built in the damper 6 constitutes the internal peripheral wall of the ring-shaped hollow section 4.
<Explanation of FIG. 30>
FIG. 30 is a view showing another disk drive having a conventional balancer.
The balancer of the disk drive shown in FIG. 30 is provided with a ring-shaped hollow section 4 and can rotate integrally with a disk 5 loaded into the disk drive.
Inside the ring-shaped hollow section 4, plural magnetic balls 1 are movably accommodated, and the ring-shaped hollow section 4 is made coaxial with the rotation center shaft 3 of a spindle motor 2. The ring-shaped hollow section 4 is formed under a turntable 7 on which the disk 5 is mounted. The external periphery of the rotor magnet 19 of the spindle motor 2 for driving the turntable 7 constitutes the internal peripheral wall of the ring-shaped hollow section 4.
<Explanation of FIG. 31>
FIG. 31 is a flowchart of a general spin-up process carried out at the time when the disk drive having the balancer is started.
In the descriptions of the present specification and claims, “a spin-up process” means a process that is carried out in the period from the time when power is supplied or a new disk is loaded into the disk drive to the time when the disk drive acquires information recorded on the disk, other than positional information, for the first time.
When power is supplied to the disk drive, or when a new disk is loaded into the disk drive, step F291 is carried out.
At step F291, initial setting is carried out. The initial setting includes the initialization of the position of an optical pickup and the adjustment of the power and the like of the semiconductor laser of the optical pickup.
The optical pickup of the disk drive is moved to a TOC (table of contents) area located near the innermost position of the disk and including a recorded table of disk information.
Furthermore, the laser power of the optical pickup is initialized. First, the value of the laser power and the position of the focus lens of the optical pickup at the time when the disk drive was driven last are set as initial setting values. These values are stored in the built-in nonvolatile memory of the disk drive. Next, the current of the laser is adjusted (power calibration) on the basis of the output signal of the power monitor photodiode built in the laser so that the output power of the laser becomes appropriate.
Next, at step F292, laser light is emitted to the disk via the object lens of the optical pickup, and the type of the disk is identified on the basis of the absolute value of the amount of the light reflected from the disk. In addition, the spindle motor is driven at a constant voltage, and the magnitude of the inertia of the disk is determined on the basis of the change at that time in the rotation speed of the disk. Furthermore, the size of the disk is determined on the basis of the magnitude of the inertia of the disk.
At step F293, adjustments are carried out for the various parameters of the electric circuits related to the optical pickup, such as an analog signal processor (hereafter referred to as “ASP”) and a digital signal processor (hereafter referred to as “DSP”). By the adjustments, the information on the disk is ready to be read properly.
At step F294, the spindle motor is controlled so that the disk is rotated synchronously at a predetermined rotation speed.
At step F295, the position of the optical pickup is finely adjusted, and seek operation is carried out to the lead-in position (the initial position of the information) of the TOC information on the disk.
At step F296, the optical pickup reads the TOC information recorded on the disk. After this, the optical pickup is generally made on standby at the 2-second position of the absolute address in the user data area, thereby being set in a standby state to wait for a command from the host.
In a disk drive having only the reproduction function in a constant rotation speed mode (hereafter referred to as a “CAV mode” (constant angular velocity mode)), the centrifugal force applied to each of the magnetic balls 1 is nearly constant in the range from the innermost periphery to the outermost periphery of the disk in one rotation speed mode. Even if the disk drive has plural rotation speed modes, the difference between the highest rotation speed and the lowest rotation speed is not so large in general. As a result, the centrifugal force applied to the magnetic ball 1 is within a constant range.
For this reason, a relatively proper balancer effect of can be obtained by the configuration and processes in accordance with the conventional example.
Furthermore, even in a disk drive having a constant linear velocity mode (hereafter referred to as a “CLV mode” (constant linear velocity mode)), in the case of a disk drive having only about three or four kinds of rotation speed modes, such as very low rotation speed modes for audio reproduction, a relatively favorable balancer effect can also be obtained by the configuration and processes in accordance with the conventional example.
Reproduction-only disk drives, such as CD-ROM drives and DVD-ROM drives, are available as examples of the above-mentioned disk drives.
However, in disk drives having various recording and reproduction speeds, for example, disk drives having both recording and reproduction functions, such as CD-RW and CD-R drives, it is impossible to obtain satisfactory results from the balancer configuration of the conventional example.
During recording wherein the rotation speed is far lower than that during reproduction, for example, the magnetic balls 1 are unstable, while rolling on the external peripheral side of the inner wall of the ring-shaped hollow section 4 or moving to the internal peripheral side of the inner wall. The magnetic balls 1 sometimes collide with the inner walls of the external or internal periphery, thereby causing impacts. As a result, a large disturbance might apply to the disk drive, instead of eliminating such a disturbance.
Furthermore, even during reproduction, during high-speed reproduction in particular, the magnetic balls 1 inside the ring-shaped hollow section 4 are pressed against the inner wall of the external periphery of the ring-shaped hollow section 4 by the centrifugal force. The balls 1 thus move stably along the inner wall of the external periphery. For this reason, the conventional balancer produces a sufficient effect. However, during intermediate-speed reproduction, during recording in particular, problems owing to the balancer are caused, instead of producing preferable results.
Embodiments will be described below.
During the spin-up process at the start of the disk drive, the rotation speed of the disk is raised from its stop state to a predetermined speed. As the rotation speed of the disk is raised, the centrifugal force applied to the magnetic ball 1 increases. When the centrifugal force applied to the magnetic ball 1 becomes larger than the magnetic attraction force of the magnet 8 as the result of the increase in rotation speed, the magnetic ball 1 separates from the magnet 8. The magnetic ball 1 then collides with the inner wall of the external periphery of the ring-shaped hollow section 4.
The impact caused at this time is applied to the disk 5.
In the case when the impact is applied during seek control, information on the disk cannot be read properly because of the impact, and traverse operation might become uncontrollable. If traverse operation becomes uncontrollable, the optical pickup collides with the internal or external periphery, whereby the optical pickup itself might be damaged physically.
In the case when an impact is applied in an on-track state (a state wherein the optical pickup is positioned on a predetermined track), the follow-up control (hereafter referred to as “servo”) of the optical pickup for the disk might become ineffective because of the impact.
Furthermore, in the case when an impact is applied during the adjustments of the various parameters of the electric circuits related to the optical pickup, the parameters might be adjusted to improper values on the basis of abnormal waveforms owing to the impact. If the disk drive wherein the parameters have been adjusted to such improper values is operated, reproduction and recording might not be carried out properly in some cases. In a disk drive having a recording function in particular, parameters and the like required to be adjusted during the spin-up process are abundant in variety. For this reason, an impact applied during the adjustments might highly increase the possibility of causing seriously improper adjustments. In addition, the time for the adjustments of the parameters and the like during the spin-up process in the disk drive having the recording function is longer than the time for the adjustments in a disk drive used only for reproduction. Hence, the probability of impact application during the adjustments becomes high, thereby increasing the frequency of occurrence of problems in the disk drive because of impacts.
In the CAV mode, however, the centrifugal force applied to the magnetic ball 1 is nearly constant. For this reason, the above-mentioned problems do not occur in a state wherein the disk rotates steadily.
However, during reproduction, recording and seek operation in the CLV mode, the centrifugal force changes since the rotation speed of the disk at the time when the pickup is at the internal periphery of the disk differs from the rotation speed at the time when the pickup is at the external periphery. For this reason, when reproduction or the like is carried out at the internal periphery of the disk, the rotation speed of ti the disk is high and the centrifugal force is large. The magnetic balls 1 might roll along the external peripheral face of the ring-shaped hollow section 4. When reproduction or the like is carried out at the external periphery of the disk, the rotation speed of the disk is low. The magnetic balls 1 might be attracted by the magnet at the internal periphery of the ring-shaped hollow section 4 and might roll along the internal peripheral face.
In the above-mentioned cases, the relationship in magnitude between the centrifugal force applied to the magnetic ball 1 and the magnetic attraction force for attracting the magnetic ball 1 by the magnet 8 is reversed somewhere on the disk. For this reason, when the pickup passes through such a position on the disk, the magnetic ball 1 separates from the magnet 8 at the internal periphery and moves to the external periphery, or separates from the external periphery and is attracted by the magnet.
The above-mentioned unstable action of the magnetic ball 1 inside the ring-shaped hollow section 4 during reproduction or the like on the disk causes adverse effects on the disk drive. For example, the unstable action of the magnetic ball 1 inside the ring-shaped hollow section 4, including the collision of the magnetic ball 1 with the inner wall of the external or internal periphery of the ring-shaped hollow section 4, applies an impact to the disk. This results in a large disturbance in the focus system and the tracking system. In particular, the unstable action and the like of the magnetic ball during reproduction or recording might deteriorate the reading performance or the writing performance of the optical pickup, or might cause a disk tracking error or the like. If an impact is applied during seek operation, servo might become ineffective or might not be made effective.
When the rotation speed of the disk is high, the magnetic ball 1 moves along the external peripheral face of the ring-shaped hollow section 4 and is located stably at an optimum balance position. As a result, the balancer functions sufficiently and cancels the imbalance amount of the disk.
However, when the rotation speed of the disk is low, the magnetic ball 1 moves along the external peripheral face of the ring-shaped hollow section 4 and is located at an optimum balance position. However, since the magnetic ball is just pressed against the external peripheral wall face by a small centrifugal force, the magnetic ball might be moved along the external peripheral wall face by a small disturbance. If the magnetic ball 1 is moved unstably along the external peripheral wall of the ring-shaped hollow section 4 in this way, the magnetic ball 1 itself causes an imbalance, instead of eliminating such an imbalance.
To solve this problem, the distance between the external peripheral face 9 and the internal peripheral face (the external peripheral face of the magnet 8) of the ring-shaped hollow section 4 is made large in the case of a disk drive having a low rotation speed mode. With this configuration, the magnetic ball 1 is located stably at an optimum balance position on the external peripheral face of the ring-shaped hollow section 4 by a large centrifugal force during high-speed rotation. As a result, it is possible to obtain a significant balancer effect.
On the other hand, in the low-speed operation mode, the magnetic ball 1 is attracted to the external peripheral face of the magnetic 8 (the internal peripheral face of the ring-shaped hollow section 4), moves along the internal peripheral face and is located stably at an optimum balance position. Since the difference between the radius of the external peripheral face and that of the internal peripheral face is large, the inertia of the magnetic ball 1 positioned on the internal peripheral face, which is applied to the disk, is smaller than the inertia of the magnetic ball 1 positioned on the external peripheral face. For this reason, even if the magnetic ball moves along the internal peripheral face during low-speed operation, the effect of the movement is limited.
However, if the distance between the external peripheral face 9 and the internal peripheral face (the external peripheral face of the magnet 8) of the ring-shaped hollow section 4 is made too large, a large impact is applied to the optical pickup when the magnetic ball 1 collide with the external or internal peripheral face. This causes the above-mentioned various problems.
In view of the above-mentioned problems, the present invention is intended to provide means and methods for attaining the stability of the balancer at various recording and reproduction speeds, not attained by using only the configuration of the conventional example, thereby to ensure operation stability at various reproduction and recording speeds.